NTSC: "National Television Standards Committee"TV signal standard used in North America, Central America, a number of SouthAmerican countries, and some Asian countries, including Japan. o 525 lines per frame o 60 half-frames per second (interlaced) = 60 Hz o Complete frame refreshed 30 times per second

PAL: "Phase Alternation by Line" TV signal standard used in the United Kingdom, most of the rest of Europe,several South American countries, some Middle East and Asian countries,several African countries, Australia, New Zealand, and other Pacific islandcountries. o 625 lines per frame o 50 half-frames per second (interlaced) = 50 Hz o Complete frame refreshed 25 times per second.

SECAM: "Sequentiel couleur avec memoire"TV signal standard still used in France, the former USSR, and some Africancountries. Until the 1980&#146s SECAM was the standard in eastern Europe,including East Germany, Poland, Czech Republic, Slovakia, and Hungary. o 625 lines per frame o 50 half-frames per second (interlaced) = 50 Hz o Complete frame refreshed 25 times per second.

In some ways the specifications of the hardware in the 8-bit Atari computerare closely linked to the specifications of the television signal standardused in the market where the machine is designed to be used. Thus there weregenerally two versions of each 8-bit Atari computer model produced: one forNTSC markets, containing NTSC versions of the ANTIC and GTIA chips, and onefor PAL markets, containing PAL versions of the ANTIC and GTIA chips.

As for SECAM versions, Piotr Fusik writes (3/06): To my knowledge, Atari had only plans or prototypes of SECAM machines. In Poland we had PAL Ataris, which was a problem at the times of SECAM. You could connect a PAL Atari to a SECAM TV, but there was no color and (IIRC) no sound. The solution was to buy an inexpensive converter mounted inside the TV, so the TV supported PAL in addition to SECAM. This was quite popular, because the VCRs were PAL, too.

Now then, what might happen if you run a software program designed with anNTSC Atari on a PAL Atari, or a program designed with a PAL Atari on an NTSCAtari? There are a number of possibilities:

1) The program may run faster or slower than intended.

All hardware timing is slightly different between NTSC and PAL machines, somost programs run slightly faster on NTSC, slightly slower on PAL. This canbe significant in applications that are computation- or timing-sensitive, suchas music players, or in any programs designed to simulate real time.

2) The program may exhibit some sort of "screen flickering" effect, or the system may completely hang.

The NTSC versions of the ANTIC chip generate a video signal with a screenrefresh rate of about 60Hz, whereas the PAL versions of the ANTIC chipgenerate a video signal with a screen refresh rate of about 50Hz. The slowerrefresh frequency of PAL machines translates into more available computationtime per screen frame. Computation-intensive software written for PALmachines that assumes more available time per screen frame than is availableon NTSC machines will not run correctly on NTSC machines.

3) The colors displayed by the program are not what was intended.

The following two paragraphs are compiled from postings by Thomas Richter:

While NTSC machines contain a single system clock crystal oscillator, in PAL machines a second oscillator that runs at 5/4 of the main system clock frequency is present to generate the color frequencies needed to drive GTIA.

This factor of 5/4 is the reason why you don&#146t get the popular "artifacted colors"/"pseudo-colors" (or, at least, not very good ones) in the ANTIC-F (Graphics 8) mode when displayed with a PAL Atari.

As a result, programs that are written with assumptions about colorartifacting effects, which vary depending upon the color CRT display deviceused, will also vary in appearance depending upon whether the machine is NTSCor PAL.

Also, the actual palettes of colors that can be generated by the computerlook somewhat different depending upon whether the machine is NTSC or PAL.

4) The program may explicitly refuse to run on incorrect hardware.

Software (some demos) may be designed to determine whether the Atari is NTSCor PAL, and refuse to run if the hardware present does not match what isexpected.

Typically, NTSC/PAL is determined by checking the "PAL" memory registerprovided by the OS, which is based on the version of GTIA that is present:

Memory location 53268 ($D014, "PAL") indicates whether the system contains an NTSC or a PAL GTIA. In Atari BASIC, PEEK(53268) returns 15 if an NTSC GTIA is present, or 1 if a PAL GTIA is present.

Alternatively, software may determine NTSC/PAL by determining how manyscanlines are being generated by ANTIC. The NTSC ANTIC generates 262scanlines, while the PAL ANTIC generates 312 scanlines. This technique isutilized by the "Numen" demo by Taquart, which refuses to run on an NTSCANTIC.

5) The program may not load correctly at all.

This would mostly likely result from copy protection techniques based uponprecise hardware timing associated with disk drives, cassette recorders, orcomponents of the computer itself, where the timing was not anticipated tovary depending upon NTSC vs. PAL hardware.

According to Jindroush (2/26/02), two examples of programs that run on NTSCmachines but not PAL machines as a result of timing-based copy protectiontechniques (probably based on vblank timing) are Transylvania and The Questby Penguin Software.

6) The program may run fine on both NTSC and PAL machines.

Either the differences are too slight to matter, or the software may besophisticated enough to detect NTSC vs PAL hardware, as described above, andact accordingly.

An examples of a program that alters its behavior depending upon detection ofNTSC versus PAL is Ghostbusters by Activision (checks for NTSC/PAL GTIA).

Bottom line:============Software written for NTSC machines (North America) will (almost) always workon PAL machines (Europe), but software designed on PAL machines won&#146tnecessarily work on NTSC machines.

Replacing the NTSC ANTIC chip in an NTSC Atari with a PAL ANTIC changes thescreen refresh rate to 50Hz, allowing most of the PAL-only European softwareto run on a North American NTSC Atari. However, make sure your display devicecan support a 50Hz PAL signal first! North American Atari users can alsoobtain and use real European PAL Atari machines, with the same caveatconcerning the display device.

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Subject: 1.15) What are the pinouts for the various ports on the Atari?